Method of metal coating and electrically heating a subterranean earth formation



United States Patent Inventors Elmond L. Claridge;

Michael Prats, Houston, Tex.

Appl. No. 813,502 Filed Patented Assignee April 4, 1969 Dec. l5, 1970 Shell Oil Company New York, N.Y. a corporation of Delaware METHOD OFMETAL COATING AND ELECTRICALLY HEATING A SUBTERRANEAN `[56] References Cited UNITED STATES PATENTS 2,118,669 5/1938 Grebe 166/248 2,267,683 12/1941 l66/292X 2,818,118 12/1957 166/248 3,137,347 6/1964 166/248 3,141,504 7/1964 Sarapuu 166/248 3,149,672 9/1964 Orkiszewski et al. 166/248 3,393,737 7/1968 Richardson 166/292 Prirmzry- Examner-jan A` Calvert Attorneys-Louis J. Bovasso and J. H. Mc Carthy ABSTRACT: A method of electrically heating a subterranean EARTH FORMATION l0 Claims, 2 Drawing Figs. earth formation by metallizing a portion of the formation and electrically connecting a source of electrical energy to the U.S. CI 166/248, metallized portion. The formation may be metallized by elec- 166/272, 166/292, 166/302 trOless metal plating and/or by introducing liquid metal. An lnt.Cl E2lb 33/138, amount of electrical current sufficient to produce heat is E21b43/20,E2lb43/24 flowed through the metallized portion of the subterranean Field of Search .i 166/248, earth formation. Fluid may be injected while the current is 272, 292, 302, 65 being applied.

*- ISV\ v V T 2? Lf' efr* l. 24 I9 2e 2o TTL-I 1.-.' i l vl, v, v', vl v( v v Pmmiufmsmm 3541192 .f w f^ INVENTORS: Y FIG 2 EDMOND L. CLARIDGE MICHAEL PRATS THEIR ATTORNEY METHOD F METAL COATING AND ELECTRICALLY HEATING A SUBTERRANEAN EARTH FORMATION BACKGROUND OF THE INVENTION l. Field of the Invention I This invention relates to the recovery of solid, liquid and gaseous carbonaceous fuels; and, more particularly, to a method of utilizing electric current to heat a subterranean earth formation.

2. Description ofthe Prior Art It is well known to apply electrical current to oil horizons and other subsurface formations to aid oil or mineral production and achieve related purposes therein. Thus, subsurface and formation heating by electrical means, electrolytic migration of subsurface fluids, linking of electrodes in subsurface formations, physically linking such electrodes bycarbonized channels, circumferential wellbore carbonization, wellbore fracturing by electrical means, etc., have all been described in the prior art, as for example in U.S. Pat. Nos. 2,795,279, 2,889,882, 3,137,347, 3,141,504, and 2,3,21 1,220. The typical complete well installations utilized in practicing such processes contemplate spaced well boreholes with discrete solid metal electrodes or electrode analogs` embedded in an earth formation or in the fluids of such an earth formation, or yet in gravel packs communicating with an earth formation whereby to transfer electrical energy to the formation or fluids thereof.

However, discrete solid metal electrodes used in such prior art processes tend to undergo localized overheating, electrode polarization, etc., that soon render them inefficient or ineffective in respect to transmitting current into the earth formations.

SUMMARY OF THE INVENTION lt is an object of this invention to provide an improved method for heating a subterranean earth formation by flowing an electric current therethrough.

lt is a further object of this invention to provide a method of controlling the electrical fracturing of a subterranean earth formation. v

lt is a still further object of this invention to-provide an improved method of consolidating an incompetentearth formation by metallizing the formation utilizing an electrical current in the process in conjunction with heating the formation.

These and other objects are preferably carried out by metallizing or metal-permeating a permeable portion of the earth formation with an electrically conductive body of metal and connecting a source of electrical energy to themetallized portion. An amount of electric current sufficient to produce heat is then flowed through the metallized portion of the subterranean earth formation.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a vertical sectional, partly schematic, view of a preferred embodiment for carrying out theconcepts of our invention; and

FIG. 2 is a vertical sectional, partly schematic, view of a method for producing hydrocarbon from a formation heated in accordance with the teachings of our invention.

DESCRIPTION of THE PREFERRED EMBODIMENT Although our invention will be described herenbelow with respect to a rubbled permeable zone within a normally impermeable subterranean earth formation, it is to be understood that the metal-permeated portion to be described may comprise either a normally permeable portion of an earth formation that is encountered by the borehole of a well, such as a reservoir sand, or a fracture-permeated or rubbled region within a normally impermeable formation. such as an oil shale.

Referring now to the drawing, FIG. 1 shows a well borehole extending into communication with a normally impermeable subterranean earth formation 11. Earth formation 1l is overlaid by an overlying earth formation 12. A rubbled area of permeable zone 13 may be formed in formation 11 surrounding the well borehole l0 by any means known in the art, such as detonating a relatively high energy explosive device in formation 11 thereby creating a chimney of rubble so as to render the formation l1 permeable. Well borehole 10 is preferably cased at casing 14 with casing 14 cemented therein, as is well known in the art. A plurality of perforations 25 are shown disposed in casing 14, thereby communicating well borehole 10 with the permeable zone 13. Obviously, the number of perforations depends on the extent of the perrneable zone 13. l

A tubing string 16 is disposed in well borehole 10 packed off from casing 14 at packing means 17. An insulated cable 18 extends through tubing string 16 and has an electrode i9 disposed at its lowermost end. Cable 18 extends out of tubing string 176 16 and is electrically connected, at its upper end, to a power source 20 for supplying electric current to electrode 19.

Electrode 19 preferably extends, at its lowermost end, into communication with a metal-permeated portion of the permeable zone 13, as for example, into a pool 21 of liquid metal. Further, formation 11 may be additionallyl metallized, as will be discussed further hereinbelow, at least within the exposed permeable portions thereof. Obviously, the particular locations for metallizing the permeable zone 13 may be selected in accordance with a predetermined schedule for heating and/or fracturing formation 11. Such metallized areas may be in the form of either liquid metal, metal plating or both.

In all embodiments of our invention, however, at least a portion of the particular earth formation being treated, such as earth formation 11, is permeated with metal. As discussed hereinabove, the permeating metal may be inthe form of a liquid that penetrates into at least the surface of the earth formation 11, such as pool 21, or metal plating 22 that is deposited on either the surfaces of the grains or the walls of the pores of a permeable zone 13. In the preferred embodiment illustrated in FIG. l, the electrical connection between power source 20 and the metal-permeated earth formation 11 is supplemented by metal plating the formation 11 (as atmetal plating 22) in addition to permeating it with liquid metal (as at pool 21).

The permeable zone 13 is preferably metal plated by circulating a metal-depositing solution through annulus outlet 23, down the annulus between tubing string 16 and casing 14, out of perforations l5 and into formation 1l, thus forming metal plating 22. Liquid metal may be introduced through tubing outlet 24, down tubing string 16 and into the' bottom of borehole 10, thus forming liquid metal pool 21. Casing 14 may be grounded as at ground 25, as is known inthe electrical art. A switch 26, for opening and closing the electrical circuit, is preferably interposed between electrode 19 and power source 20. A ground 27 completes the circuit between power source 20 and electrode 19 as illustrated in FIG. 1.

ln operation, upon actuation of switch 26, the circuit is closed and electric current flows from power source 20 through electrode 19 and into pool 21. The dashed lines in FIG. l indicate the flow path of electric current from pool 21 through the metal plating 22 to casing 14. An amount of current is flowed sufficient to produce heat and thus increase the permeability of permeable zone 13 for subsequent production of hydrocarbons therefrom.

Where the natural formation is impermeable as illustrated in FIG. 1, the metal-plating solution may be spotted and held in the rubbled portion of the formation to be plated. Suitable metal-deposition solutions are described in U.S. Pat. No. 3,393,737 to Richardson, directed to an electroless metal deposition process. In such a situation, a first portion of the metal-plating solution may be kept static for a time sufficient to become depleted and then displaced with a fresh batch of solution in the lmanner described in a copending application to Richardson Ser. No. 692,726, filed Dec. 22, 1967 now U.S. Pat. No. 3,500,926.

-Where the earth formation is normally permeable and no ceation of a permeable zone is required, the electroless metal-plating technique disclosed in the Richardson patent is preferred. In such a situation, the permeable zone would be similar to zone 13 of FIG. l, but would be permeated by fluids that flow radially in the manner described in the aforementioned Richardson patent.

."A'Where an electroless metal-plating process is used, a highly conductive metal plating, such as a copper plating, is preferred. Where a liquid metal is used, it may comprise substantially any metal or metallic alloy which is liquid in the environment of the subsurface earth formation being treated. It may be spotted in the bottom of the well borehole, as illus- (rated in FIG. l, and injected into the rubbled portion of an impermeable earth formation, also as illustrated in FIG. l, by pressuring the tubing string I6 while allowing liquid metal solution to enter the annulus through annulus outlet 23 at a point above packing means 17 A metallic substance such as a metal or metallic alloy that has both a relatively low melting point and a relatively high boiling point, for example a metal such as gallium, is particularly suited for use in the carrying outpf the concepts of our invention. The density contrast between a liquefied metal and a fluid such as water, which would normally be used in conventional fluid injection processes for displacing our solution into formation Il surrounding well borehole l0, ensures the deposition of the liquefied metal as discussed hereinabove.

Y, Where the earth formation being treated is normally permeable,` and a liquid metal is used, the pressure within the tubing string 17 is preferably maintained within general limits. Duringljlthe electrical-heating operation, the pressure in tubing siting' 17 is preferably maintained too low to displace all of the liquefied metal out of well borehole l and into earth formation' vl l, and too high to allow the formation pressure to back flowenough of the metal into the well borehole l0 to establish a contact between it and a metal conduit that has a lower voltage potential.

The heating of permeable zone 13 serves to solidify loose sandl grain particles disposed in permeable zone 13. Thus, the techniques of our invention may be applied to the consolidation of loose or incompetent subsurface earth formations.

/Referring now to FIG. 2, wherein like numerals'refer to like parts of FIG. l, a second well borehole 28 is illustrated spaced from well borehole and extending into communication with formation '11. Well borehole 28 is casedat casing 29 with the casing cemented therein as is well known in the art. A tubing strinfg 30'is disposed in well borehole 28 and packed off at packing means 3l. A plurality of perforations 32 are provided in'lcasing 29 in the manner discussed hereinabove with respect to, fperforations l5. An annulus outlet 33 is provided at the u r end of casing 29; a tubing string outlet 34 is similarly ded at the upper end of tubing string 30. Both outlets 33 34 are coupled to suitable conduits (not shown) for in- -cing fluids into and flowing fluids out of formation Il, as

,Y 'iquid metal pool 35 is shown disposed at the lower end of w borehole 28. Pool 35 is similar to pool 2l of well borehole formed in the manner discussed hereinabove with respect to powcil21. ln like manner, metal plating 36, similar to metal platl2, is shown previously formed in the permeable zone 37 ofiij'ell borehole 28, all in the manner discussed hereinabove, with respect to well borehole l0.

flii'order to produce fluids from formation i l, both permeaones 13 and 37 are extended until they intersect as illustrated on FIG. 2. This may be accomplished by electrically heating both zones in the manner disclosed hereinabove until such intersection is obtained. The respective pools 2l and 35, andmetal plating 22 and 36, also intersect at this point. For convenience of illustration, it is to be understood that metal plating 22 is extended tofintersect with plating 36 in such a manner that the regions between well boreholes It) and 28 are suitably metal-platedflnt'his manner, the loose sand grain parthe well boreholes l0 and 28, while electricity is also passed into the formation via the electrodes 22, 36. High current densities (amperes per square centimeter of borehole area or of external electrode area) can thus be achieved without overheating of the rock or sand formation Il in the vicinity of the electrode 22, 36. vThe injected fluid, preferably water of any convenient composition, carries the excess heat away from the vicinity of the wellbores 10 and 28. Besides this, the injected fluid thus heated will warm and transport oil or other valuable material from a first well borehole towards a second wellbore used for recovery of these materials. The attainment Iof high current densities permits the heating, at an appreciable rate, of oil or other valuable material at a significant distance away from the wellbore. For example, with a current density of 1A; ampere per square centimeter at the outer surface of a porous, metallized sand electrode l meter in radius (such as metal plating 22 and 36), a typical rock formation can be electrically heated at a rate of about l C./day at a radius of 100 meters from the well. Such current density could not be maintained without cooling, as the temperature rise around the perimeter of the electrode would otherwise be about 1 C./second.

A similar process may be carried out in wellbore 10 of FIG. l by injecting fluid throughfmetal plating 2l and 22 while flowing electricity therethrough. f

The electrification of both zones 13 and 37 (FIG. 2) may be l stopped and formation fluids may be flowed from formation 11 through perforations 32, up the annulus formed between tubing string 30 and casing 29 of well borehole 28, and out of annulus outlet 33. Suitable valves (not shown) may be provided for decreasing the overburden pressure so that fluids are recovered from formation 11, all in the `manner well-known in the art. Hydrocarbons may then be separated from the recovered formation fluids by passing such fluids through suitable separation means as illustrated in FIG. 2.

We claim:

l.. A method of electrically heating a subterranean earth formation comprising the steps'of:

providing on a permeable portion of said subterranean earth formation a coating of electrically conductive body of metal; thereafter,

electrically connecting a source of electrical energy to the metal coated portion of said subterranean earth forma tion; and

flowing an amount of electric current sufficient to produce heat through said metal-coated portion of said subterranean earth formation.

2. The method of claim 1 including the step of first extending a well borehole into communication with said earth formation; and wherein the step of metal-coating portion of said earth formation includes the step of injecting a permeating liquid metal down said well borehole and into contact with said formation.

3. The method of' claim 2 wherein the step of metal-coating a portion of said earth formation includes the step of injecting a liquid metal-plating solution into the formation.

d. The method of claim 3 wherein the step of injecting a liquid metal-plating solution includes the step'of injecting a metal-plating solution containing a highly conductive metal into the formation.

5. The'method of claim 2 wherein the step of injecting a per meating liquid metal includes the step of injecting sufficient liquid metal to form a pool that penetrates into at least a portion of said earth formation.

6. The method of claim 5 wherein the step of injecting liquid fmetal to form a pool includes the step of injecting a metallic metal-coated portion.

9. The method of claim l wherein the step of electrically connecting a source of electric energy includes the step of providing an electrode extending from the surface of the earth into contact with the metal-coated portion of said earth formation.

10. The method of claim l including the step of heating said formation by injecting fluid through said metal-coated portion while electric current is being flowed therethrough. 

